High temperature CCR process with integrated reactor bypasses

ABSTRACT

A process is presented for increasing the aromatics content in a reformate process stream. The process modifies existing processes to change the operation without changing the reactors or heating units. The process includes bypasses to utilize heating capacity of upstream heating units, and passes the excess capacity of the upstream heating units to downstream process streams.

FIELD OF THE INVENTION

The present invention relates to processes for the production ofaromatic compounds from a hydrocarbon stream. In particular, the processis an improvement to increase the amount of aromatic compounds such asbenzene, toluene and xylenes in a hydrocarbon feedstream.

BACKGROUND OF THE INVENTION

The reforming of petroleum raw materials is an important process forproducing useful products. One important process is the separation andupgrading of hydrocarbons for a motor fuel, such as producing a naphthafeedstream and upgrading the octane value of the naphtha in theproduction of gasoline. However, hydrocarbon feedstreams from a rawpetroleum source include the production of useful chemical precursorsfor use in the production of plastics, detergents and other products.

The upgrading of gasoline is an important process, and improvements forthe conversion of naphtha feedstreams to increase the octane number havebeen presented in U.S. Pat. Nos. 3,729,409; 3,753,891; 3,767,568;4,839,024; 4,882,040; and 5,242,576. These processes involve a varietyof means to enhance octane number, and particularly for enhancing thearomatic content of gasoline.

While there is a move to reduce the aromatics in gasoline, aromaticshave many important commercial uses. Among them include the productionof detergents in the form of alkyl-aryl sulfonates, and plastics. Thesecommercial uses require more and purer grades of aromatics. Theproduction and separation of aromatics from hydrocarbons streams areincreasingly important.

Processes include splitting feeds and operating several reformers usingdifferent catalysts, such as a monometallic catalyst or a non-acidiccatalyst for lower boiling point hydrocarbons and bi-metallic catalystsfor higher boiling point hydrocarbons. Other improvements include newcatalysts, as presented in U.S. Pat. Nos. 4,677,094; 6,809,061; and7,799,729. However, there are limits to the methods and catalystspresented in these patents, and which can entail significant increasesin costs.

Improved processes are needed to reduce the costs and energy usage inthe production of aromatic compounds.

SUMMARY OF THE INVENTION

The present invention is a process for the reformation of hydrocarbonsin a hydrocarbon process stream. In particular, the present invention isfor the improvement of existing systems to increase the aromatic contentof a hydrocarbon feedstream. The process includes the change inoperation of an existing system of reforming reactors, and theredirection of process streams within a reforming reactor system.

The process is for increasing the aromatics content of the hydrocarbonstream, and includes passing the hydrocarbon stream through a series ofreactors and reactor feed heaters. The process includes operating thefirst reactor at a lower temperature, and passing the excess capacity ofthe heating units for the first feedstream to downstream flows. Theheated feedstream is split into at least two portions, and the firstportion is passed to a reforming reactor. The second portion is passedto a downstream reactor effluent stream and is further heated forpassing a feedstream with added heat to a downstream reactor.

In one embodiment, the first reactor is operated at a first inlettemperature, and the subsequent downstream reactors are operated at atemperature that is greater than the first inlet temperature.

In one embodiment, the process stream is split before the first reactorheater, and a portion is heated to a temperature greater than the firstreactor inlet temperature. The heated portion is further split to pass aportion downstream, while mixing another portion with the unheatedportion to form the first reactor feedstream.

Other objects, advantages and applications of the present invention willbecome apparent to those skilled in the art from the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram of a first embodiment of the invention for utilizingupstream reactors to heat feed for downstream processing; and

FIG. 2 is a diagram of a second embodiment of the invention forutilizing upstream reactors to heat feeds for downstream processing.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to improving the yields of aromaticsfrom a hydrocarbon feedstream. In particular, the improvement is for anaphtha feedstream where the hydrocarbons are reformed to increase theyields of aromatics in the C6 to C8 range. The process is aimed atimproving existing processes without the requirement of building newequipment. The present invention increases the production of aromaticsin existing hydrocarbon reforming units. This is done by reducing theinlet temperature to a first reactor, and increasing the inlettemperature of the reactor feeds to downstream reactors. This shifts theheating duty of upstream heating units to downstream reactors, withoutthe need to replace existing heating units or reactors.

There is an increased demand for aromatics. Important aromatics includebenzene, toluene, and xylenes. These aromatics are important componentsin the production of detergents, plastics, and other high valueproducts. With increasing energy costs, energy efficiency is animportant aspect for improving the yields of aromatics. The presentinvention provides for understanding the differences in the propertiesof the different components in a hydrocarbon mixture to develop a betterprocess.

The dehydrogenation and aromatization process of converting hydrocarbonstreams lean in aromatics to hydrocarbon streams rich in aromatics is anendothermic process with the addition of energy to maintain usefulreaction temperatures. The process requires a series of reactors withreactor interheaters. One of the problems is the ability to providesufficient downstream heat to the process stream. The present inventionallows for the shifting of heating loads on a process stream todownstream reactors without replacing expensive heaters or reactors.

A hydrocarbon stream is comprised of many constituents, and eachconstituent behaves differently under different conditions. Theconstituents can be divided into larger classes of compounds, where oneclass, such as paraffins, comprises many different paraffinic compounds.The dehydrogenation process is an endothermic process which requires acontinuous input of energy to heat the process stream in the reactor.The greater the endothermicity, the greater the temperature drop withinthe reactor, and therefore the greater the amount of heat that is to beadded to maintain the reaction. The dropping of temperature reduces thereaction rate and reduces the conversion. This requires additional heatto maintain a desired reaction rate.

Among the constituents in the hydrocarbon stream, the amount ofendothermicity varies considerably. Energy usage in the dehydrogenationprocess can be reduced by separating out the individual constituents,but would be increased in the endeavor to separate the constituents.However, the reaction rates for the different constituents, and for thedifferent classes of compounds varies. These variations change withtemperature, such that different reactions, and different operatingtemperatures allow for a partial selectivity of the dehydrogenationprocess over some constituents and classes of compounds.

Compounding problems in the dehydrogenation process are the conversionrates for some of the constituents. In order to achieve good conversionof C6 and C7 paraffins to aromatic compounds, high temperatures andrelatively short contact times are required. With the highendothermicity, control and maintenance of high reaction temperaturescan be difficult. The hydrocarbon stream of primary interest is a fullboiling range naphtha having olefins, naphthenes, paraffins, andaromatics, and the process is aimed at converting the non-aromatics tohigher value aromatic compounds.

The present invention provides bypasses to shift the excess dutyavailable in upstream heaters, such as a charge heater, or combined feedexchanger, to downstream reactor feeds. The reactor section bypassesreduces the required modifications to downstream reactors in order tooperate at higher reactor inlet temperatures.

In one embodiment of the present invention, the process includes passinga hydrocarbon process stream through a series of reactors and reactorfeed heaters. At least one of the heated feed streams is split into atleast two portions. A first portion is passed to a corresponding reactorto generate a reactor effluent stream. The second portion is combinedwith a downstream reactor effluent stream, and the combined stream ispassed to a downstream reactor feed heater to generate a downstreamreactor feedstream. The last reactor in the series generates a productstream that has an increased aromatics content.

The new process shifts the temperatures of the feedstreams to thereactors with the first reactor operated at a first temperature, andsubsequent reactors in the series operated at a temperature that isgreater than the first temperature.

In one optional configuration, the process includes splitting at leastone reactor effluent stream into at least two portions, a first portionand a second portion. The first portion of the effluent stream is passedwith a second portion of an upstream heated feedstream to a reactorinterheater. The second portion of the effluent stream is combined witha downstream heated feedstream and passed to a downstream reactor. Thedownstream reactor can be the next reactor in the series, or thedownstream can be the second reactor downstream of the effluent stream.

In one embodiment, the process is as shown in FIG. 1. This embodimentutilizes four reactors for the reforming process, but can be expanded toinclude more reactors, or adjusted to operate with fewer reactors. Theprocess includes passing a hydrocarbon process stream 10 through acharge heater 20 to generate a first heated feedstream 22. The heatedfeedstream 22 is split into two portions, a first portion 22 a and asecond portion 22 b.

The first portion 22 a is passed to a first reactor 30 to generate afirst effluent stream 32. The first effluent stream 32 is combined withthe second portion 22 b and passed through a first reactor interheater40 to generate a second heated feedstream 42. The second heatedfeedstream 42 is split into two portions, a first portion 42 a and asecond portion 42 b. The first portion 42 a is passed to a secondreactor 50 to generate a second effluent stream 52. The second effluentstream 52 is combined with the second portion 42 b and passed to asecond reactor interheater 60 to generate a third heated feedstream 62.The third heated feedstream 62 is split into two portions, a firstportion 62 a and a second portion 62 b. The first portion is passedthrough a third reactor 70 to generate a third effluent stream 72. Thethird effluent stream 72 is combined with the second portion 62 b andpassed to a third reactor interheater 80 to generate a fourth heatedfeedstream 82. The fourth heated feedstream 82 is passed to a fourthreactor 90 to generate a product stream 92.

The process of the present invention can include additional bypasses toprovide further control of the inlet temperatures, and to increase theability to pass head duty to downstream reactor feeds. In a variation,the process includes passing the product stream 92 through a combinedfeed heat exchanger 100 to generate a cooled product stream 102. Thefeedstream 10 is preheated to generate a preheated feedstream 12. Thepreheated feedstream 12 can be split into two portions, a first portion14 and a second portion 16. The first portion 14 is passed through thecharge heater 20 to heat the feedstream 14 to a temperature greater thanthe inlet feed temperature to the first reactor 30, generating theheated feedstream 22. The heated feedstream 22 is split, as above, intotwo portions with the second portion 22 b passed to a downstreaminterheater. The first portion 22 a is combined with the second portion16 of the preheated feedstream to reduce the temperature of the secondportion 22 a before passing the reactor feed to the first reactor 30.

The feed to the first reactor 30 comprises a combination of the firstportion 22 a of the heated feedstream and a second portion 16 of thepreheated feedstream. This allows for heating the first portion 14 ofthe preheated feedstream to a temperature greater than the first reactorinlet temperature. The charge heater 20 can add additional heat to thefirst portion 14 wherein the added heat will be transferred todownstream reactors. A temperature indicator controller 26 will controlthe amount of the second portion 16 of the preheated feedstream to bemixed with the first portion 22 a of the heated feedstream to being thetemperature to the desired first reactor inlet temperature. Thisprovides an advantage for utilizing excess capacity in the charge heater20 to supplement heat to downstream reactors, without having to addadditional heaters. Temperature indicator controllers can be utilizedwith downstream reactors for mixing a portion of effluent streams fromupstream reactors with a portion of streams heated by interheaters.

The present invention is operated such that the first reactor isoperated at a first inlet temperature and subsequent reactors areoperated at a second inlet temperature greater than the first reactorinlet temperature. When referring to temperatures, for the reformingprocess, the controls refer to the inlet temperatures, as thetemperature in the reactor declines as the reaction proceeds. The firstinlet temperature is less than 540° C., with a preferred inlettemperature between 400° C. and 500° C., and with a more preferredtemperature between 400° C. and 550° C. The second inlet temperature isgreater than 500° C., with a preferred inlet temperature between 510° C.and 600° C., and with a more preferred temperature between 520° C. and560° C.

In one aspect of the invention the inlet temperatures of the reactorsare operated at successively increasing temperatures, with the inlettemperature of the first reactor between 450° C. and 520° C., and thetemperature of the subsequent reactors between 500° C. and 600° C.

A second embodiment can be seen with FIG. 2. A hydrocarbon feedstream110 is split into a first portion 114 and a second portion 116. Thefirst portion 114 is passed through a charge heater 120 to generate afirst heated feedstream 122. The first heated feedstream 122 is splitinto a first portion 122 a and a second portion 122 b. The first portion122 a of the heated feedstream is combined with the second portion 116of the hydrocarbon feedstream, and the combined stream is passed to afirst reactor 130 to generate a first reactor effluent stream 132. Thefirst reactor effluent stream 132 is split into a first portion 132 aand a second portion 132 b. The first portion 132 a is passed through afirst reactor interheater 140 to generate a first heated effluent stream142. The first heated effluent stream 142 is split into a first portion142 a and a second portion 142 b. The first portion 142 a and the secondportion 132 b are combined to form a second reactor 150 feedstream, andthe second reactor 150 generates a second reactor effluent stream 152.The second reactor effluent stream 152 is combined with the secondportion 122 b of the first heated feedstream 122 and passed through asecond reactor interheater 160 to generate a second heated effluentstream 162. The second heated effluent stream 162 is passed to a thirdreactor 170 to generate a third effluent stream 172. The third reactoreffluent stream 172 is combined with the second portion 142 b of thefirst heated effluent stream 142 and the combined stream is passed to athird reactor interheater 180 to generate a third heated effluent stream182. The third heated effluent stream 182 is passed to a fourth reactor190 to generate an effluent product stream 192.

The process can be further expanded to cover additional reactors andadditional interheaters within a reforming reactor system.

The product stream 192 can further be passed to a combined feed heatexchanger 200 to generate a cooled product stream 202. The hydrocarbonfeedstream 110 can be passed through the heat exchanger 200 to generatea preheated feedstream 112.

The process is designed to upgrade existing systems, by allowing theexcess heat capacity to be passed downstream, and by operating the firstreactor at a temperature below the temperatures of the subsequentreactors. In an alternate operation, each subsequent inlet reactortemperature is greater than the inlet reactor temperature of thepreceding reactor.

The temperature of operation is the inlet temperature of the firstreactor feed, which is a combined feed of 122 a and 166, and istypically a temperature between 450° C. and 540° C. The space velocitycan be increased over normal commercial operating conditions. Thereaction conditions include a liquid hour space velocity (LHSV) of thepresent invention in the range from 0.6 hr⁻¹ to 10 hr⁻¹. Preferably, theLHSV is between 0.6 hr⁻¹ and 5 hr⁻¹, with a more preferred value between1 hr⁻¹ and 5 hr⁻¹. The catalyst also has a residence time in thereformer between 0.5 hours and 36 hours.

The present invention lowers the first inlet temperature to the firstreactor to a temperature less than 540° C., with subsequent reactorshaving inlet temperatures greater than 540° C. The first reactor inlettemperature is preferred to be between 400° C. and 500° C., with a morepreferred inlet temperature between 400° C. and 450° C. The inlettemperature to the subsequent reactors, or second and greater reactorsin the series should be greater than 500° C., with a preferred inlettemperature between 510° C. and 600° C., and a more preferred inlettemperature between 520° C. and 560° C.

Due to the elevated temperature, the problems of potential increasedthermal cracking can be addressed by having a shorter residence time ofthe hydrocarbon process stream in the equipment at the elevatedtemperature, or by moving higher temperatures to downstream reactors.The increased temperature can also increase coking on metallic surfacesof the transfer equipment and the reactor internals.

The process can also include adding compounds to change the ability toreduce the amount of coking. One example is the injection of a sulfurcompound, such as HOS, into the feedstream. The presence of a smallamount of sulfur reduces the coking in the high temperature reforming.

The reforming process is a common process in the refining of petroleum,and is usually used for increasing the amount of gasoline. The reformingprocess comprises mixing a stream of hydrogen and a hydrocarbon mixtureand contacting the resulting stream with a reforming catalyst. The usualfeedstock is a naphtha feedstock and generally has an initial boilingpoint of about 80° C. and an end boiling point of about 205° C. Thereforming reaction converts paraffins and naphthenes throughdehydrogenation and cyclization to aromatics. The dehydrogenation ofparaffins can yield olefins, and the dehydrocyclization of paraffins andolefins can yield aromatics.

The reforming process is an endothermic process, and to maintain thereaction, the reformer is a catalytic reactor that can comprise aplurality of reactor beds with interbed heaters. The reactor beds aresized with the interbed heaters to maintain the temperature of thereaction in the reactors. A relatively large reactor bed will experiencea significant temperature drop, and can have adverse consequences on thereactions. The interbed heaters reheat the process stream as the processstream flows from one reactor bed to a sequential reactor bed within thereformer reactor system. The most common type of interbed heater is afired heater that heats the fluid and catalyst flowing in tubes. Otherheat exchangers can be used.

Reforming catalysts generally comprise a metal on a support. The supportcan include a porous material, such as an inorganic oxide or a molecularsieve, and a binder with a weight ratio from 1:99 to 99:1. The weightratio is preferably from about 1:9 to about 9:1. Inorganic oxides usedfor support include, but are not limited to, alumina, magnesia, titania,zirconia, chromia, zinc oxide, thoria, boria, ceramic, porcelain,bauxite, silica, silica-alumina, silicon carbide, clays, crystallinezeolitic aluminasilicates, and mixtures thereof. Porous materials andbinders are known in the art and are not presented in detail here. Themetals preferably are one or more Group VIII noble metals, and includeplatinum, iridium, rhodium, and palladium. Typically, the catalystcontains an amount of the metal from about 0.01% to about 2% by weight,based on the total weight of the catalyst. The catalyst can also includea promoter element from Group IIIA or Group IVA. These metals includegallium, germanium, indium, tin, thallium and lead.

While the invention has been described with what are presentlyconsidered the preferred embodiments, it is to be understood that theinvention is not limited to the disclosed embodiments, but it isintended to cover various modifications and equivalent arrangementsincluded within the scope of the appended claims.

The invention claimed is:
 1. A process for increasing the aromaticcontent in a naphtha feedstream having olefins, naphthenes, paraffins,and aromatic in reforming reactors in a series, comprising: passing thenaphtha feedstream to a charge heater to generate a first heated stream;passing a portion of the first heated stream to a first reformingreactor to generate a first effluent stream; passing the first effluentstream and a second portion of the first heated stream to a firstreforming reactor interheater to generate a second heated stream;passing a first portion of the second heated stream to a secondreforming reactor to generate a second effluent stream; passing thesecond effluent stream and a second portion of the second heated streamto a second reforming reactor interheater to generate a third heatedstream; and passing a first portion of the third heated stream to athird reforming reactor to generate a third effluent stream to produce aproduct stream by converting paraffin and naphthenes in the naphthafeedstream through dehydrogenation and cyclization in the presence ofadded hydrogen, added sulfur compounds and a reforming catalyst inreforming reactors to aromatics; wherein the first reforming reactor isoperated at a temperature between 400° C. and 500° C., and the second,third reforming reactors are operated at a second reaction temperaturebetween 500° C. and 600° C., and wherein the second reaction temperatureis greater than the first reaction temperature; wherein the reformingreactors are operated as successively greater temperatures.
 2. Theprocess of claim 1, further comprising: passing the third effluentstream and a second portion of the third heated stream to a thirdreactor interheater to generate a fourth heated stream; and passing thefourth heated stream to a fourth reforming reactor to generate a fourthreactor effluent stream.
 3. The process of claim 2 further comprisingpassing the fourth reactor effluent stream to subsequent downstreamreforming reactors.
 4. The process of claim 1 further comprising passingthe third reactor effluent stream to subsequent downstream reformingreactors.
 5. The process of claim 1 further comprising; passing thereactor product stream through a feed heat exchanger to generate acooled product stream; and passing the naphtha feedstream through thefeed head exchanger to preheat.
 6. The process of claim 1 wherein thesecond reaction temperature is between 520° C. and 560° C.